If the previous dial attempt was unsuccessful, then all the new dial attempts are skipped
until the background goroutine determines that the given address can be successfully dialed.
This reduces query latency when some of vmstorage nodes are unavailable and dialing them is slow.
This should help with https://github.com/VictoriaMetrics/VictoriaMetrics/issues/711
This commit is based on ideas from the https://github.com/VictoriaMetrics/VictoriaMetrics/pull/2756
The main differences are:
- The check for healthy/unhealthy storage nodes is moved one level lower from app/vmselect/netstorage to lib/netutil.ConnPool.
This makes possible re-using this feature everywhere lib/netutil.ConnPool is used.
- The check doesn't take into account handshake errors for already established connections.
Handshake errors usually mean improperly configured VictoriaMetrics cluster, so they shouldn't be ignored.
This should reduce potential spikes in the number of established connections in the following cases:
- when the connection establishing procedure becomes temporarily slow
- after a temporary spike in the rate of ConnPool.Get() calls
See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2552
